Manufacturing method of light emitting device

ABSTRACT

A method of manufacturing a light emitting device, including the steps of: forming an active layer composed of a compound semiconductor containing indium by a vapor phase growth method; and forming a cap layer composed of a compound semiconductor on said active layer by a vapor phase growth method at a growth temperature approximately equal to or lower than a growth temperature for said active layer.

This application is a divisional of prior application Ser. No.08/847,471, filed Apr. 25, 1997 now U.S. Pat. No. 5,990,496.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device and amanufacturing method thereof.

2. Description of the Background Art

Light emitting devices such as light emitting diodes and semiconductorlaser devices which are formed of III-V group nitride systemsemiconductors such as GaN, AlGaN, InGaN and InAlGaN are receiving agreat deal of attention because they are capable of, by directtransition, light emission in the yellow to ultraviolet region,especially in the blue region, with large luminous intensity.

FIG. 8 is a schematic cross-sectional view showing a conventional lightemitting diode composed of III-V group nitride system semiconductors.

In FIG. 8, formed in order on a sapphire substrate 101 are a GaN bufferlayer 102, an n-type GaN contact layer 103 also serving as an n-typecladding layer, an InGaN active layer 104, a p-type AlGaN cladding layer105, and a p-type GaN contact layer 106. A p electrode 107 is formed onthe p-type GaN contact layer 106 and an n electrode 108 is formed on then-type GaN contact layer 103.

The individual layers of this light emitting diode are grown by metalorganic chemical vapor deposition (MOCVD) at the growth temperaturesshown in Table 1, for example.

TABLE 1 Name of layer Growth temperature (° C.) Buffer layer 102 600N-type contact layer 103 1150 Active layer 104 860 P-type cladding layer105 1150 P-type contact layer 106 1150

When manufacturing this light emitting diode, the p-type AlGaN claddinglayer 105 is formed on the InGaN active layer 104 at a growthtemperature higher than that for the InGaN active layer 104 to achievegood crystallinity. The growth of the p-type AlGaN cladding layer 105 atsuch a high temperature causes elimination of constituent elements suchas In from the InGaN active layer 104. The crystallinity of the InGaNactive layer 104 is thus deteriorated when crystal-growing the p-typeAlGaN cladding layer 105. This causes difficulty in achieving largerluminous intensity with the light emitting diode.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a light emitting devicehaving high luminous intensity and its manufacturing method.

A light emitting device according to the present invention includes, inthis order, a first cladding layer composed of a compound semiconductorof a first conductivity type, an active layer composed of a compoundsemiconductor containing indium, a cap layer composed of a compoundsemiconductor, and a second cladding layer composed of a compoundsemiconductor of a second conductivity type.

In the light emitting device of the invention, formation of the caplayer on the active layer suppresses elimination of constituent elementssuch as indium from the active layer. This provides increased luminousintensity.

The first cladding layer is composed of a nitride system semiconductorof the first conductivity type, the active layer is composed of anitride system semiconductor, the cap layer is composed of a nitridesystem semiconductor, and the second cladding layer is composed of anitride system semiconductor of the second conductivity type.

The first cladding layer may be composed of a III-V group nitride systemsemiconductor of the first conductivity type, the active layer of aIII-V group nitride system semiconductor, the cap layer of a III-V groupnitride system semiconductor, and the second cladding layer of a III-Vgroup nitride system semiconductor of the second conductivity type. Itis preferable to form the cap layer on the entire surface of the activelayer in close contact.

The active layer may be composed of an InGaN layer. This providesremarkable effect since indium is susceptible to elimination. The caplayer may be formed of an AlGaN layer, and is preferably formed of a GaNlayer.

The cap layer of Al_(u)Ga_(1−μ)N, and the second cladding layer ofAl_(z)Ga_(1−z)N of the second conductivity type, wherein the Alcomposition ratio u of the cap layer is preferably smaller than the Alcomposition ratio z of the second cladding layer. It is preferable fromthe point of view of manufacturing yield that the first cladding layeris formed of GaN.

Particularly, it is more preferable that the Al composition ratio u ofthe cap layer is approximately 0.1 or smaller. It is more preferablethat the cap layer is formed of GaN. In this case, the cap layer formedof a GaN layer suppresses elimination of constituent elements such asindium from the active layer. This provides significantly largerluminous intensity.

The cap layer preferably has a larger bandgap than the active layer.This prevents the cap layer from serving as a light emitting region.

It is preferable that the cap layer has a bandgap intermediate betweenthose of the active layer and the second cladding layer. This allowsreduction of the operating voltage.

It is preferable that the cap layer has impurity concentration lowerthan that of the second cladding layer. This reduces the possibility ofundesirable impurity diffusion from the cap layer side into the activelayer, thus suppressing deterioration of luminous intensity due toundesirable impurity diffusion.

Particularly, it is more preferable that the cap layer is an undopedlayer. This allows almost no undesirable impurity diffusion from the caplayer side into the active layer. This sufficiently suppresses luminousintensity deterioration due to undesirable impurity diffusion.

It is preferable that the cap layer has a thickness of approximately notless than 200 Å and approximately not more than 400 Å. This providessignificantly increased luminous intensity.

The first cladding layer may be formed on a substrate composed of asemiconductor or an insulator with a buffer layer composed ofAl_(x)Ga_(1−x)N interposed therebetween, and the Al composition ratio xof the buffer layer is preferably larger than 0 and not larger than 1.This improves the manufacturing yield.

Particularly, it is more preferable that the Al composition ratio x ofthe buffer layer is 0.4 or larger, and smaller than 1. This furtherimproves the manufacturing yield. It is still more preferable that theAl composition ratio x of the buffer layer is not less than 0.4, and notmore than 0.6. This still further improves the manufacturing yield.

The light emitting device may further include an under-layer composed ofAl_(y)Ga_(1−y)N between the buffer layer and the first cladding layer,wherein the Al composition ratio y of the underlayer is preferably 0 orlarger, and smaller than 1. This improves the manufacturing yield.

A method of manufacturing a light emitting device according to anotheraspect of the present invention includes the steps of forming an activelayer composed of a compound semiconductor containing indium by a vaporphase growth method and forming a cap layer composed of a compoundsemiconductor on the active layer by a vapor phase growth method at atemperature approximately equal to or lower than a growth temperaturefor the active layer.

According to the manufacturing method of the invention, formation of thecap layer on the active layer at a growth temperature approximatelyequal to or lower than the growth temperature for the active layersuppresses elimination of constituent elements such as indium from theactive layer. This provides larger luminous intensity.

The manufacturing method of the present invention may further includethe step of forming a cladding layer composed of a compoundsemiconductor on the cap layer by a vapor phase growth method at agrowth temperature higher than the growth temperature allowing crystalgrowth of the active layer.

The active layer may be composed of a nitride system semiconductor andthe cap layer of a nitride system semiconductor. The cladding layer maybe formed of a nitride system semiconductor of one conductivity type.

The active layer may be composed of a III-V group nitride systemsemiconductor and the cap layer of a III-V group nitride systemsemiconductor. The cladding layer may be formed of a III-V group nitridesystem semiconductor of one conductivity type. Particularly, the activelayer may be formed of an InGaN layer. In this case, a remarkable effectis obtained since indium is susceptible to elimination.

It is preferable that the cap layer is composed of Al_(u)Ga_(1−u)N, thecladding layer is composed of Al_(z)Ga_(1−z)N of one conductivity type,and that the Al composition ratio u of the cap layer is smaller than theAl composition ratio z of the cladding layer.

Particularly, it is preferable that the Al composition ratio u of thecap layer is approximately 0.1 or smaller. It is more preferable thatthe cap layer is composed of GaN. In this case, since the cap layer isformed of a GaN layer, elimination of constituent elements such asindium from the active layer is suppressed, thus providing significantlylarger luminous intensity.

Particularly, it is preferable that the cap layer is an undoped layer.In this case, there is almost no possibility a of diffusion ofundesirable impurities from the cap layer side to the active layer side.This sufficiently suppresses deterioration of luminous intensity due toundesirable impurity diffusion.

It is preferred that the cap layer has a thickness of approximately notsmaller than 200 Å and approximately not larger than 400 Å. This enablesremarkable improvement of the luminous intensity.

It is preferable to form the cap layer at a growth temperatureapproximately equal to that for the active layer. This allows the caplayer to be continuously formed without a time interval after formationof the active layer, which considerably prevents elimination ofconstituent elements from the active layer.

The growth temperature for the cap layer is preferably set to atemperature which allows crystal growth of the active layer. The activelayer is preferably formed at a growth temperature not lower than 700°C. and not higher than 950° C. The cap layer is preferably formed at agrowth temperature not lower than 700° C. and not higher than 950° C.The formation of the cap layer on the active layer at a low growthtemperature suppresses elimination of constituent elements such asindium from the active layer.

It is preferable that the active layer has a quantum well structureincluding an InGaN quantum well layer and a GaN quantum barrier layerand the GaN quantum barrier layer is formed by a vapor phase growthmethod at a growth temperature not lower than 700° C. and not higherthan 950°. In this case, elimination of constituent elements such asindium from the InGaN quantum well layer is suppressed, thus enablinglarger luminous intensity. An InGaN having an In composition ratio lowerthan that of the quantum well layer may be used as the quantum barrierlayer.

A method of manufacturing a light emitting device according to stillanother aspect of the present invention includes the steps of forming afirst cladding layer composed of a compound semiconductor of a firstconductivity type by a vapor phase growth method, forming an activelayer composed of a compound semiconductor containing indium by a vaporphase growth method on the first cladding layer, forming a cap layercomposed of a compound semiconductor on the active layer by a vaporphase growth method at a growth temperature approximately equal to orlower than a temperature allowing vapor phase growth of the activelayer, and forming a second cladding layer composed of a compoundsemiconductor of a second conductivity type on the cap layer by a vaporphase growth method at a temperature higher than the temperatureallowing vapor phase growth of the active layer.

The first cladding layer may be composed of a nitride systemsemiconductor of the first conductivity type, the active layer of anitride system semiconductor, the cap layer of a nitride systemsemiconductor, and the second cladding layer of a nitride systemsemiconductor of the second conductivity type.

The first cladding layer may be formed of a III-V group nitridesystem-semiconductor of the first conductivity type, the active layer ofa III-V group nitride system semiconductor, the cap layer of a III-Vgroup nitride system semiconductor, and the second cladding layer of aIII-V group nitride system semiconductor of the second conductivitytype.

It is preferable to form a buffer layer composed of a non-single-crystalIII-V group nitride system semiconductor and a single-crystal underlayercomposed of an undoped III-V group nitride system semiconductor in thisorder on a substrate and then perform crystal growth for the firstcladding layer, the active layer, the cap layer and the second claddinglayer. It is preferable that the buffer layer is formed of AlGaN. Thebuffer layer may be formed of AlN. The underlayer is preferably formedof GaN and the underlayer may be formed of AlGaN.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional diagram of a light emitting diodeaccording to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional diagram of a light emitting diodeaccording to a third embodiment of the present invention.

FIG. 3 is a schematic cross-sectional diagram of a semiconductor laserdevice according to a fourth embodiment of the present invention.

FIG. 4 is a schematic cross-sectional diagram of a semiconductor laserdevice according to a fifth embodiment of the present invention.

FIG. 5 is a schematic cross-sectional diagram of a semiconductor laserdevice according to a sixth embodiment of the present invention.

FIG. 6 is a schematic cross-sectional diagram showing an example of astructure to which the present invention can be applied.

FIG. 7 is a schematic cross-sectional diagram showing another example ofa structure to which the present invention is applicable.

FIG. 8 is a schematic cross-sectional diagram of a conventional lightemitting diode.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A light emitting diode composed of III-V group nitride systemsemiconductors according to a first embodiment of the present inventionwill now be described in detail referring to FIG. 1.

In FIG. 1, formed in order on a sapphire insulating substrate 1 are a110-Å-thick undoped Al_(x)Ga_(1−x)N (x=0.5) buffer layer 2, a0.2-μm-thick undoped GaN underlayer 3, a 4-μm-thick Si-doped n-type GaNcontact layer 4 also serving as an n-type cladding layer, and a0.2-μm-thick Zn- and Si-doped In_(q)Ga_(1−q)N (q=0.05) active layer 5.Formed in order on the InGaN active layer 5 are a 200-Å-thick undopedGaN cap layer 6 for preventing crystal deterioration of the active layer5, a 0.15-μm-thick Mg-doped p-type Al_(z)Ga_(1−z)N (z=0.2) claddinglayer 7, and a 0.3-μm-thick Mg-doped p-type GaN contact layer 8.

The part from the p-type GaN contact layer 8 to a certain position inthe n-type GaN contact layer 4 is removed, so that the n-type GaNcontact layer 4 is exposed. A p electrode 9 composed of Au is formed onthe upper surface of the p-type GaN contact layer 8 and an n electrode10 composed of Al is formed on the n electrode formation region wherethe n-type GaN contact layer 4 is exposed.

A method of manufacturing the above-described light emitting diode willbe explained. In this embodiment, the individual layers are formed bymetal organic chemical vapor deposition (MOCVD).

First, the substrate 1 is placed in a metal organic chemical vapordeposition apparatus. Then, with the substrate 1 held at a non-singlecrystal growth temperature, e.g., a growth temperature (a substratetemperature) of 600° C., the non-single-crystal undoped AlGaN bufferlayer 2 is grown on the substrate 1 by using H₂ and N₂ as carrier gasand ammonia, trimethylgallium (TMG) and trimethylaluminum (TMA) asmaterial gas.

Subsequently, with the substrate 1 held at a single crystal growthtemperature, or a growth temperature preferably of 1000-1200° C., e.g.,1150° C., the single-crystal undoped GaN underlayer 3 is grown on thebuffer layer 2 by using H₂ and N₂ as carrier gas and ammonia andtrimethylgallium (TMG) as material gas.

Then with the substrate 1 held at a single crystal growth temperature,or a growth temperature preferably of 1000-1200° C., e.g., 1150° C., thesingle-crystal Si-doped n-type GaN contact layer 4 is grown on theunderlayer 3 by using H₂ and N₂ as carrier gas, ammonia andtrimethylgallium (TMG) as material gas, and SiH₄ as dopant gas.

Next, with the substrate 1 held at a single crystal growth temperature,or preferably at a growth temperature of 700-950° C., e.g., at 860° C.,the single-crystal Si- and Zn-doped InGaN active layer 5 is grown on then-type contact layer 4 by a1) using H₂ and N₂ as carrier gas, ammonia,triethylgallium (TEG) and trimethylindium (TMI) as material gas, andSiH₄ and diethylzinc (DEZ) as dopant gas.

Subsequently, with the substrate 1 held at a temperature equal to orlower than the growth temperature for the active layer 5, or at 860° C.in this embodiment, the single-crystal undoped GaN cap layer 6 is grownon the InGaN active layer 5 continuously following the growth of theactive layer 5 by using H₂ and N₂ as carrier gas, and ammonia andtrimethylgallium (TMG) as material gas. Triethylgallium (TEG) may beused in place of trimethylgallium (TMG).

Then with the substrate 1 held at a single crystal growth temperature,i.e., preferably at a growth temperature of 1000-1200° C., e.g.. at1150° C., the single-crystal Mg-doped p-type AlGaN cladding layer 7 isgrown on the GaN cap layer 6 by using H₂ and N₂ as carrier gas, ammonia,trimethylgallium (TMG) and trimethylaluminum (TMA) as material gas, andCp₂Mg (cyclopentadienylmagnesium) as dopant gas.

Next, with the substrate 1 held at a single crystal growth temperature,i.e., preferably at a growth temperature of 1000-1200° C., e.g., at1150° C., the single-crystal Mg-doped p-type GaN contact layer 8 isgrown on the p-type cladding layer 7 by using H₂ and N₂ as carrier gas,ammonia and trimethylgallium (TMG) as material gas, and Cp₂Mg(cyclopentadienylmagnesium) as dopant gas.

After the crystal growth, the substrate 1 is taken out from theapparatus and the part from the p-type contact layer 8 to the midway inthe n-type contact layer 4 is removed by reactive ion beam etching (RIE)to form the n electrode formation region in which the n-type contactlayer 4 is exposed.

Then a heat treatment is performed at 750-800° C. for 30-60 minutes inan atmosphere of nitrogen to activate the dopants in the p-type contactlayer 8 and the p-type cladding layer 7 to obtain high carrierconcentration and to correct crystal deterioration in the n-type contactlayer 4 caused by the etching.

Then the p electrode 9 composed of Au is formed by evaporation, or thelike, on the p-type contact layer 8 and the n electrode 10 composed ofAl is formed by evaporation or the like on the n electrode formationregion of the n-type contact layer 4. A heat treatment at 500° C. isthen applied to cause the p electrode 9 and the n electrode 10 to comeinto ohmic contact with the p-type contact layer 8 and the n-typecontact layer 4, respectively, to form the light emitting diode shown inFIG. 1.

This light emitting diode, having the undoped GaN cap layer 6 in closecontact with the InGaN active layer 5, prevents elimination ofconstituent elements such as In from the InGaN active layer 5 in orafter formation of the active layer 5. This reduces the number ofcrystal defects in the active layer 5, suppressing deterioration of thecrystallinity.

Furthermore, it is thought that undesirable impurity diffusion into theactive layer 5 is suppressed since it has a less number of crystaldefects.

Moreover, since the GaN cap layer 6 of this embodiment is a so-calledundoped layer formed without intentional use of dopant, undesirableimpurity diffusion into the InGaN active layer 5 is sufficientlysuppressed.

As discussed above, in this embodiment, the effect of suppressingimpurity diffusion into the active layer 5 is produced because thenumber of crystal defects in the active layer 5 is reduced bysuppressing elimination of constituent elements from the active layer 5and the effect of suppressing impurity diffusion into the active layer 5is produced because the cap layer 6 is an undoped layer which remarkablysuppresses undesirable impurity diffusion into the active layer 5.

Accordingly, while light emitting diodes having the same structure asthis embodiment except that they have no cap layer 6 suffer from largevariations in light emission wavelength, no light emission or low lightemission, the light emitting diode of this embodiment achieves smallvariations in the light emission wavelength and considerably increasedluminous intensity.

Particularly, when manufacturing the light emitting diode of thisembodiment, the undoped GaN cap layer 6 is grown right on the entiresurface of the InGaN active layer 5 at a temperature not higher than thegrowth temperature for the InGaN active layer 5. This not only preventselimination -7 constituent elements of the InGaN active layer 5 whenforming the cap layer 6 but also prevents elimination of constituentelements from the InGaN active layer 5 after formation of the cap layer6. Accordingly, the manufacturing method of this embodiment isdesirable.

Especially, in this embodiment, continuously growing the InGaN activelayer 5 and the GaN cap layer 6 at approximately equal growthtemperatures sufficiently suppresses elimination of constituent elementsfrom the InGaN active layer 5 and mass productivity is improved.

With the aforementioned structure, the luminous intensity was 340(arbitrary unit) with a 200-Å-thick GaN cap layer 6. With a 100-Å-thickGaN cap layer 6, the luminous intensity was 36 (arbitrary unit). This islarger than that of a structure having no cap layer 6, but is aboutone-tenth that of the 200-Å-thick cap layer 6. With a 300-Å-thick GaNcap layer 6, the luminous intensity was 1.4 times that of the200-Å-thick one, and with a 400-Å-thick GaN cap layer 6, it was 0.8times that of the 200-Å-thick one.

This suggests that a preferable effect is obtained when the GaN caplayer 6 has a thickness between 200-400 Å, or that it is preferable thatthe GaN cap layer 6 has a thickness large enough to cause almost noquantum effect.

In this embodiment, the non-single-crystal AlGaN buffer layer 2 isformed on the substrate 1 and then the undoped GaN single-crystalunderlayer 3 is formed under single crystal growth conditions. Thiseasily provides the underlayer 3 with remarkably improved surfaceconditions, which suppresses leakage current of the device and increasesmanufacturing yield of the devices.

When a GaN layer is used as the non-single-crystal buffer layer 2, it islikely to suffer from pits in the surface, which may lead to throughdefects. It is therefore undesirable to use a GaN layer as the bufferlayer 2 from the point of view of the manufacturing yield. As anon-single crystal buffer layer 2 used in combination with the undopedsingle-crystal underlayer 3, use of an AlN layer is preferable in thepoint of view of the manufacturing yield, and the use of an AlGaN layeris the most desirable.

The surface conditions and FWHM (Full Width Half Maximum) of X-raydiffraction spectrum were measured with AlGaN layers having various Alcomposition ratios. Table 2 below shows the measurements.

TABLE 2 Al composition Surface conditions X-ray FWHM (arcsec) 1.0 good550 0.8 good 504 0.6 good 451 0.4 good 390 0.2 many pits 428 0 many pitsunknown

The results in Table 2 show that it is desirable that the AlGaN layerhas an Al composition ratio of 0.4 or greater, and smaller than 1, andmore desirably, not smaller than 0.4 nor larger than 0.6.

As the undoped single-crystal underlayer 3, an AlGaN layer may be usedin place of the GaN layer, but an AlN layer is not preferable because itis likely to suffer from cracking on the surface.

Next, a light emitting diode formed of III-V group nitride systemsemiconductors in a second embodiment of the present invention will bedescribed.

This embodiment differs from the first embodiment in that it uses a200-Å-thick undoped Al_(u)Ga_(1−u)N layer as the cap layer 6 in place ofthe undoped GaN layer. The value of u is approximately 0.1 and 0.2. ThisAl_(u)Ga_(1−u)N layer, too, is formed by MOCVD at the same temperatureas the growth temperature for the active layer 5, at 860° C. in thisembodiment. H₂ and N₂ are used as carrier gas and ammonia,trimethylgallium (TMG) and trimethylaluminum (TMA) are used as materialgas. Triethylgallium (TEG) may be used instead of trimethylgallium(TMG).

It was seen that the light emitting diode of this embodiment alsoprovides remarkably larger luminous intensity than a light emittingdiode having no cap layer 6.

However, as compared with the 200-Å-thick undoped GaN cap layer 6 in thefirst embodiment regarded as providing a luminous intensity of 450(arbitrary unit), an undoped Al_(u)Ga_(1−u)N cap layer 6 with an Alcomposition ratio u of about 0.1 in the second embodiment provided aluminous intensity smaller than half thereof, 190 (arbitrary unit).

With an undoped Al_(u)Ga_(1−u)N cap layer 6 having an Al compositionratio u of about 0.2, the luminous intensity was one-third that for theAl composition ratio u of 0.1.

This shows that it is the most preferable to use a GaN layer as the caplayer 6 and that when using an Al_(u)Ga_(1−u)N layer, a small Alcomposition ratio u as 0.1 is preferable. The larger an Al compositionratio is, the larger the bandgap of an AlGaN is. The Al compositionratio of the p-type cladding layer 7 is 0.2 as described in the firstembodiment. When the Al composition ratio of the cap layer 6 is 0.1, thebandgap of the cap layer 6 is smaller than that of the p-type claddinglayer 7. From this, it is understood that it is preferable that the caplayer 6 has a bandgap between that of the active a layer 5 and that ofthe p-type cladding layer 7.

Next, a light emitting diode composed of III-V group nitride systemsemiconductors in a third embodiment of the invention will be describedreferring to FIG. 2.

This embodiment differs from the first embodiment in that it uses no GaNunderlayer 3, whose manufacturing method is the same as that in thefirst embodiment except that it excludes the process step for formingthe GaN underlayer 3.

While the light emitting diode of this embodiment provides lower yieldthan the light emitting diode of the first embodiment, it achieveslarger luminous intensity than a light emitting diode having no caplayer 6.

Although the light emitting diodes of the above-described embodimentshave the active layer 5 on the n-type contact layer 4, an n-type AlGaNcladding layer may be provided between the n-type contact layer 4 andthe active layer 5. An n-type AlGaN cladding layer and an n-type InGaNlayer may be provided between the n-type contact layer 4 and the activelayer 5.

The aforementioned embodiments use an active layer with anon-quantum-well structure as the active layer 5, rather than aquantum-well structure. However, needless to say, an active layer with asingle-quantum-well structure or a multi-quantum-well structure may beused. For example, the active layer may have a single-quantum-wellstructure formed of an In_(z)Ga_(1−z)N (1>s>0) quantum well layer, or amulti-quantum-well structure formed of an In_(z)Ga_(1−z)N (1>s>0)quantum well layer and an In_(r)Ga_(1−r)N (1>s>r≧0) quantum barrierlayer.

When using a multi-quantum-well structure formed of an In_(s)Ga_(1−s)N(1>s>0) quantum well layer and a GaN quantum barrier layer, it ispreferable to form the GaN quantum barrier layer at a growth temperaturenot lower than 700° C. nor higher than 950° C., and it is alsopreferable to grow the quantum well layer and the quantum barrier layerat approximately equal growth temperatures.

Although the light emitting diodes of the embodiments use an Si- andZn-doped active layer 5, an undoped active layer may be used.

Next, an index guided semiconductor laser device in a fourth embodimentof the present invention will be explained referring to FIG. 3. Thissemiconductor laser device is a self-aligned semiconductor laser device.

In FIG. 3, formed in order on a sapphire insulating substrate 11 are anundoped AlGaN buffer layer 12 with a thickness of about 100-200 Å, anundoped GaN underlayer 13 with a thickness of 0.4 μm, an n-type GaNcontact layer 14 with a thickness of 4 μm, and an n-type AlGaN claddinglayer 15 with a thickness of 0.1-0.5 μm. Formed in order on the n-typeAlGaN cladding layer 15 are an InGaN active layer 16, an undoped GaN caplayer 17 with a thickness of 200-400 Å, and a p-type AlGaN claddinglayer 18 with a thickness of 0.1-0.5 μm.

An n-type GaN or n-type AlGaN current blocking layer 19 with a thicknessof 0.2-0.3 μm having a stripe-like opening in the center part is formedon the p-type AlGaN cladding layer 18. A p-type GaN contact layer 20having a thickness of 0.1-0.5 μm is formed on the top surface and in thestripe-like opening of the n-type current blocking layer 19.

A p electrode 21 is formed on the p-type GaN contact layer 20 and an nelectrode 22 is formed on the n-type GaN contact layer 14.

As the active layer 16, a non-quantum-well structure layer may be used,or a single-quantum-well structure layer or a multi-quantum-well layermay be used. In the case of a non-quantum-well structure layer, thethickness is set to about 0.1 to 0.3 μm. In the case of asingle-quantum-well structure layer, the thickness of the quantum welllayer is set to 10-50 Å, and in the case of a multi-quantum-wellstructure layer, the thickness of the quantum well layer is set to 10-50Å and the thickness of the quantum barrier layer is set to about 10-100Å,

This semiconductor laser device is manufactured by performing crystalgrowth once by using chemical vapor deposition, such as MOCVD. Whenmanufacturing, the undoped AlGaN buffer layer 12 is formed at a growthtemperature or 600° C., the undoped GaN underlayer 13, the n-type GaNcontact layer 14 and the n-type AlGaN cladding layer 15 are formed at agrowth temperature of 1150° C., the InGaN active layer 16 and the GaNcap layer 17 are formed at a growth temperature of 700-950° C., and thep-type AlGaN cladding layer 18, the n-type current blocking layer 19 andthe p-type GaN contact layer 20 are formed at a growth temperature of1150° C.

The semiconductor laser device of this embodiment also provides largerluminous intensity than a semiconductor laser device having no cap layer17.

Next, an index guided semiconductor laser device according to a fifthembodiment of the invention will be explained referring to FIG. 4. Thissemiconductor laser device is a ridge-buried type semiconductor laserdevice.

In FIG. 4, formed in order on a sapphire insulating substrate 31 are anundoped AlGaN buffer layer 32 with a thickness of 100-200 Å, an undopedGaN underlayer 33 with a thickness of 0.4 μm, an n-type GaN contactlayer 34 with a thickness of 4 μm, and an n-type AlGaN cladding layer 35with a thickness of 0.1-0.5 82 m. Formed in order on the n-type AlGaNcladding layer 35 are an InGaN active layer 36, an undoped GaN cap layer37 with a thickness of 200-400 Å, and a p-type AlGaN cladding layer 38with a thickness of 0.1-0.5 μm. The InGaN active layer 36 has the samestructure and thickness as the InGaN active layer 16 in the fourthembodiment.

The p-type AlGaN cladding layer 38 has a flat region and a ridge regionformed in the center of the flat region. A p-type GaN cap layer 39having a thickness of 0.1 μm is formed on the ridge region of the p-typeAlGaN cladding layer 38. An n-type GaN or n-type AlGaN current blockinglayer 40 having a thickness of 0.2-0.3 μm is formed on the upper surfaceof the flat region and the side surfaces of the ridge region of thep-type AlGaN cladding layer 38 and on the side surfaces of the p-typecap layer 39. A p-type GaN contact layer 41 having a thickness of0.1-0.5 μm is formed on the p-type cap layer 39 and the n-type currentblocking layer 40.

A p electrode 42 is formed on the p-type GaN contact layer 41 and an nelectrode 43 is formed on the n-type GaN contact layer 34.

This semiconductor laser device is manufactured by performing crystalgrowth three times by using chemical vapor deposition such as MOCVD.When manufacturing, the undoped AlGaN buffer layer 32 is formed at agrowth temperature of 600° C., the undoped GaN underlayer 33, the n-typeGaN contact layer 34 and the n-type AlGaN cladding layer 35 are formedat a growth temperature of 1150° C., the InGaN active layer 36 and theundoped GaN cap layer 37 are formed at a growth temperature of 700-950°C., and the n-type AlGaN cladding layer 38, the p-type cap layer 39, then-type current blocking layer 40 and the p-type GaN contact layer 41 areformed at a growth temperature of 1150° C.

The semiconductor laser device of this embodiment also provides largerluminous intensity than a semiconductor laser device having no cap layer37.

Next, a gain guided semiconductor laser device according to a sixthembodiment of the invention will be described referring to FIG. 5.

In FIG. 5, formed in order on a sapphire insulating substrate 51 are anundoped AlGaN buffer layer 52 having a thickness of 100-200 Å, anundoped GaN underlayer 53 having a thickness of 0.4 μm, an n-type GaNcontact layer 54 having a thickness of 4 μm, and an n-type AlGaNcladding layer 55 having a thickness of 0.1-0.5 μm.

Formed in order on the n-type AlGaN cladding layer 55 are an InGaNactive layer 56, an undoped GaN cap layer 57 having a thickness of200-400 Å, a p-type AlGaN cladding layer 58 having a thickness of0.1-0.5 μm, and a p-type GaN contact layer 59 having a thickness of0.1-0.5 μm. The InGaN active layer 56 has the same structure andthickness as the InGaN active layer 16 in the fourth embodiment.

An SiO₂, SiN, or n-type GaN current blocking layer 60 having astripe-like opening in the center is formed on the p-type GaN contactlayer 59. A p electrode 61 is formed on the p-type GaN contact layer 59and an n electrode 62 is formed on the n-type GaN contact layer 54.

The semiconductor laser device of this embodiment is formed byperforming crystal growth once by using chemical vapor deposition suchas MOCVD. When manufacturing, the undoped AlGaN buffer layer 52 isformed at a growth temperature of 600° C., the undoped GaN underlayer53, the n-type GaN contact layer 54 and the n-type AlGaN cladding layer55 are formed at a growth temperature of 1150° C., the InGaN activelayer 56 and the undoped GaN cap layer 57 are formed at a growthtemperature of 700-950° C., and the p-type AlGaN cladding layer 58 andthe p-type GaN contact layer 59 are formed at a growth temperature of1150° C.

The semiconductor laser device of this embodiment, too, provides largerluminous intensity than a semiconductor laser device having no cap layer57.

Although the first to sixth embodiments have shown light emittingdevices having semiconductor layers on an insulating substrate, thepresent invention can be similarly applied to light emitting deviceshaving semiconductor layers on a conductive substrate such as an SiCsubstrate and electrodes on the top surface of the uppermost layer ofthe semiconductor layers and on the lower surface of the substrate.

Although an active layer, a cap layer and a p-type cladding layer areformed in this order on an n-type cladding layer in the structuresexplained above, an active layer, a cap layer and an n-type claddinglayer may be formed in this order on a p-type cladding layer. That is tosay, the individual layers in the first to sixth embodiments may havethe opposite conductivity types.

The first to sixth embodiments have described applications of thisinvention to light emitting devices such as light emitting diodes andsemiconductor laser devices, but the present invention is alsoapplicable to semiconductor devices having a compound semiconductorlaser containing In such as field effect transistors.

With the structure shown in FIG. 6, for example, an n-type AlGaN layer72 and an InGaN layer 73 are formed in order on an n-type GaN layer 71and a p-type SiC layer 75 is formed above the InGaN layer 73 with anundoped GaN cap layer 74 therebetween. In this case, the InGaN layer 73and the GaN cap layer 74 are formed at a growth temperature of 700-950°C. and the p-type SiC layer 75 is formed at a growth temperature of1300-1500° C. In this example, as well, formation of the undoped GaN caplayer 74 on the InGaN layer 73 suppresses elimination of constituentelements such as In from the InGaN layer 73.

In the structure of FIG. 7, an InGaN layer 82 is formed on an n-type SiClayer 81 and a p-type SiC layer 84 is formed above the InGaN layer 82with an undoped GaN cap layer 83 therebetween. In this case, as well,the InGaN layer 82 and the undoped GaN cap layer 83 are formed at agrowth temperature of 700-950° C. and the p-type SiC layer 84 is formedat a growth temperature of 1300-1500° C. In this example, as well,formation of the undoped GaN cap layer 83 on the InGaN layer 82suppresses elimination of constituent elements such as In from the InGaNlayer 82.

The light emitting diodes of the first to third embodiments can beapplied to light sources for use in optical fiber communication systems,light sources for use in photocouplers, monochromatic or polychromaticpilot lamps, light sources for use in display devices such as digitaldisplays, level meters and displays, light sources for use in facsimiledevices, printer heads, signal lamps, lamps for use in automobiles suchas high-beam lamps, liquid-crystal televisions, back-light sources foruse in liquid-crystal displays, amusement systems, and so on.

The semiconductor laser devices of the fourth to sixth embodiments canbe applied to laser surgical knives, light sources for use in opticalcommunication systems, light sources for use in optical pick-up devicesin disk systems for DVD (Digital Video Disk) and the like, light sourcesfor use in color laser beam printers, light sources for use in laserprocessing devices, light sources for laser holographies, light sourcesfor laser displays, light sources for amusement systems, and so on.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

1. A method of manufacturing a light emitting device, comprising thesteps of: forming an active layer composed of a nitride systemsemiconductor by a vapor phase growth method; forming a cap layercomposed of a nitride system semiconductor on said active layer by avapor phase growth method at a growth temperature approximately equal toor lower than a growth temperature for said active layer; and forming acladding layer composed of a nitride system semiconductor of oneconductivity type on said cap layer by a vapor phase growth method;wherein said cap layer has a lower impurity concentration than saidcladding layer.
 2. The method of manufacturing a light emitting deviceaccording to claim 1, wherein said active layer is composed of a III-Vgroup nitride system semiconductor, said cap layer is composed of aIII-V group nitride system semiconductor, and said cladding layer iscomposed of a III-V group nitride system semiconductor.
 3. The method ofmanufacturing a light emitting device according to claim 2, wherein saidstep of forming a cladding layer includes forming said cladding layer ata growth temperature higher than the temperature allowing crystal growthof said active layer.
 4. The method of manufacturing a light emittingdevice according to claim 3, wherein said cap layer is composed ofAl_(u)Ga_(1−u)N, said cladding layer is composed of Al_(z)Ga_(1−z)N ofone conductivity type, and the Al composition ratio u of said cap layeris smaller than the Al composition ratio z of said cladding layer. 5.The method of manufacturing a light emitting device according to claim4, wherein the Al composition ratio u of said cap layer is approximatelyequal to or smaller than 0.1.
 6. The method of manufacturing a lightemitting device according to claim 1, wherein said cap layer is anundoped layer.
 7. The method of manufacturing a light emitting deviceaccording to claim 1, wherein said cap layer has a thickness ofapproximately not smaller than 200 Å nor larger than 400 Å.
 8. Themethod of manufacturing a light emitting device according to claim 1,wherein the step of forming said cap layer includes forming said caplayer at a growth temperature of not lower than 700° C. nor higher than950° C.
 9. The method of manufacturing a light emitting device accordingto claim 1, wherein said step of forming said cap layer includes formingsaid cap layer at a growth temperature approximately equal to the growthtemperature for said active layer.
 10. The method of manufacturing alight emitting device according to claim 1, wherein said active layer iscomposed of InGaN.
 11. The method of manufacturing a light emittingdevice according to claim 1, wherein said active layer has a quantumwell structure including an InGaN quantum well layer and a GaN quantumbarrier layer, and the step of forming said active layer includesforming said GaN quantum barrier layer at a growth temperature of notlower than 700° C. nor higher than 950° C.
 12. A method of manufacturinga light emitting device, comprising, in the following order, the stepsof: forming a buffer layer composed of a nitride based compoundsemiconductor on a substrate; forming an underlayer composed of anitride based compound semiconductor; forming a first cladding layercomposed of a nitride based compound semiconductor of a firstconductivity type; forming an active layer composed of a nitride basedcompound semiconductor containing indium; forming a cap layer composedof AlGaN; forming a second cladding layer composed of a nitride basedcompound semiconductor of a second conductivity type at a growthtemperature higher than that of said active layer, wherein said step offorming the active layer includes forming a quantum well structureincluding a quantum well layer and quantum barrier layer.
 13. The methodaccording to claim 12, further comprising the step of forming a contactlayer of the first conductivity type on said underlayer.
 14. The methodaccording to claim 13, wherein said step of forming the contact layer ofthe first conductivity type includes forming said contact layer of thefirst conductivity type at a growth temperature of not lower than 1000°C. nor higher than 1200° C.
 15. The method according to claim 12,further comprising the step of forming a contact layer of the secondconductivity type on said second cladding layer.
 16. The methodaccording to claim 15, wherein said step of forming the contact layer ofthe second conductivity type includes forming a contact layer of thesecond conductivity type composed of GaN.
 17. The method according toclaim 12, wherein said step of forming said quantum well structureincludes forming a quantum well layer composed of In_(s) Ga _(1−s) Nwherein 1>s>0.
 18. The method according to claim 12, wherein said stepof forming the quantum well structure includes forming a quantum welllayer composed of In_(s) Ga _(1−s) N wherein 1>s>0, and a quantumbarrier layer composed of In _(r) Ga _(1−r) N wherein 1>s>r≧0.
 19. Themethod according to claim 12, wherein said step of forming the cap layerincludes forming a cap layer having an Al composition ratio of at most0.1.
 20. A method of manufacturing a light emitting device, comprising,in the following order, the steps of: forming a buffer layer composed ofa nitride based compound semiconductor on a substrate; forming anunderlayer composed of a nitride based compound semiconductor; forming afirst cladding layer composed of a nitride based compound semiconductorof a first conductivity type; forming an active layer composed of anitride based compound semiconductor containing indium; forming a caplayer composed of AlGaN; forming a second cladding layer composed of anitride based compound semiconductor of a second conductivity type at agrowth temperature higher than that of said active layer, wherein saidstep of forming the cap layer includes forming a cap layer having abandgap between those of said active layer and said second claddinglayer.
 21. A method of manufacturing a light emitting device,comprising, in the following order, the steps of: forming a buffer layercomposed of a nitride based compound semiconductor on a substrate;forming an underlayer composed of a nitride based compoundsemiconductor; forming a first cladding layer composed of a nitridebased compound semiconductor of a first conductivity type; forming anactive layer composed of a nitride based compound semiconductorcontaining indium; forming a cap layer composed of AlGaN; forming asecond cladding layer composed of a nitride based compound semiconductorof a second conductivity type at a growth temperature higher than thatof said active layer, wherein said step of forming the cap layerincludes forming a cap layer having an impurity concentration lower thanthat of said second cladding layer.
 22. The method according to claim12, wherein said step of forming the cap layer includes forming anundoped cap layer.
 23. The method according to claim 12, wherein saidstep of forming the cap layer includes forming a cap layer having athickness of not smaller than 200 Å nor larger than 400 Å.
 24. Themethod according to claim 12, wherein said step of forming the secondcladding layer includes forming a second cladding layer composed ofAlGaN.
 25. The method according to claim 24, wherein said step offorming the cap layer includes forming a cap layer having an Alcomposition ratio smaller than that of said second cladding layer. 26.The method according to claim 12, wherein said step of forming the caplayer includes forming as said cap layer a layer suppressing eliminationof the indium from said active layer.
 27. The method according to claim12, wherein said step of forming the underlayer includes forming anunderlayer composed of Al_(y) Ga _(1−y) N, and the Al composition ratioy of said underlayer is at least 0 and smaller than
 1. 28. The methodaccording to claim 12, wherein said step of forming the buffer layerincludes forming a buffer layer composed of Al_(x) Ga _(1−x) N, and theAl composition ratio x of said buffer layer is larger than 0 and at most1.
 29. The method according to claim 28, wherein said step of formingthe buffer layer includes forming a buffer layer having an Alcomposition ratio x of not smaller than 0.4 nor larger than 0.6.
 30. Themethod according to claim 12, wherein said step of forming the activelayer includes forming an active layer composed of InGaN.
 31. The methodaccording to claim 12, wherein said step of forming the active layerincludes forming said active layer at a growth temperature of not lowerthan 700° C. nor higher than 950° C.
 32. The method according to claim12, wherein said step of forming the second cladding layer includesforming said second cladding layer at a growth temperature of not lowerthan 1000° C. nor higher than 1200° C.
 33. The method according to claim12, wherein said step of forming the first cladding layer includesforming a first cladding layer composed of AlGaN.
 34. The methodaccording to claim 12, wherein said step of forming the cap layerincludes forming said cap layer at a growth temperature substantiallyequal to or lower than that of said active layer.
 35. The methodaccording to claim 12, wherein said step of forming the cap layerincludes forming said cap layer at a growth temperature of not lowerthan 700° C. nor higher than 950° C.
 36. A method of manufacturing alight emitting device, comprising, in the following order, the steps of:forming a buffer layer composed of a nitride based compoundsemiconductor on a substrate; forming an underlayer composed of anitride based compound semiconductor; forming a first cladding layercomposed of a nitride based compound semiconductor of a firstconductivity type; forming an active layer composed of a nitride basedcompound semiconductor containing indium; forming a cap layer composedof AlGaN; forming a second cladding layer composed of a nitride basedcompound semiconductor of a second conductivity type at a growthtemperature higher than that of said active layer, wherein said step offorming the underlayer includes forming an undoped underlayer.
 37. Themethod according to claim 12, wherein said step of forming the bufferlayer includes forming a non-single crystalline buffer layer.
 38. Themethod according to claim 12, wherein said step of forming theunderlayer includes forming a single crystalline underlayer.
 39. Themethod according to claim 12, wherein said step of forming the cap layerincludes forming the cap layer containing Al.
 40. The method accordingto claim 12, wherein said step of forming the cap layer includes forminga cap layer having a band gap larger than that of said active layer. 41.A method of manufacturing a light emitting device, comprising, in thefollowing order, the steps of: forming a buffer layer composed of anitride based compound semiconductor; forming an underlayer composed ofa nitride based compound semiconductor; forming a contact layer composedof a first conductivity type; forming a first cladding layer composed ofa nitride based compound semiconductor of the first conductivity type;forming an active layer having a quantum well structure including aquantum well layer and a quantum barrier layer and composed of a nitridebased compound semiconductor containing indium; forming a cap layercomposed of a nitride based compound semiconductor; forming a secondcladding layer composed of a nitride based compound semiconductor of asecond conductivity type at a growth temperature higher than that ofsaid active layer.
 42. The method according to claim 41, wherein saidstep of forming the contact layer of the first conductivity typeincludes forming said contact layer of the first conductivity type at agrowth temperature of not lower than 1000° C. nor higher than 1200° C.43. The method according to claim 41, further comprising the step offorming a contact layer of the second conductivity type on said secondcladding layer.
 44. The method according to claim 41, wherein said stepof forming the contact layer of the second conductivity type includesforming a contact layer of the second conductivity type composed of GaN.45. The method according to claim 41, wherein said step of forming theactive layer includes forming a quantum well layer composed of In_(s) Ga_(1−s) N wherein 1>s>0.
 46. The method according to claim 41, whereinsaid step of forming the active layer includes forming a quantum welllayer composed of In_(s) Ga _(1−s) N wherein 1>s>0, and a quantumbarrier layer composed of In _(r) Ga _(1−r) N wherein 1>s>r≧0.
 47. Themethod according to claim 41, wherein said step of forming the cap layerincludes forming a cap layer having an Al composition ratio of at most0.1.
 48. The method according to claim 41, wherein said step of formingthe cap layer includes forming a cap layer having a bandgap betweenthose of said active layer and said second cladding layer.
 49. Themethod according to claim 41, wherein said step of forming the cap layerincludes forming a cap layer having an impurity concentration lower thanthat of said second cladding layer.
 50. The method according to claim41, wherein said step of forming the cap layer includes forming anundoped cap layer.
 51. The method according to claim 41, wherein saidstep of forming the cap layer includes forming a cap layer having athickness of not smaller than 200 Å nor larger than 400 Å.
 52. Themethod according to claim 41, wherein said step of forming the secondcladding layer includes forming a second cladding layer composed ofAlGaN.
 53. The method according to claim 52, wherein said step offorming the cap layer includes forming a cap layer having an Alcomposition ratio smaller than that of said second cladding layer. 54.The method according to claim 41, wherein said step of forming the caplayer includes forming as said cap layer a layer suppressing eliminationof the indium from said active layer.
 55. The method according to claim41, wherein said step of forming the underlayer includes forming anunderlayer composed of Al_(y) Ga _(1−y) N, and the Al composition ratioy of said underlayer is at least 0 and smaller than
 1. 56. The methodaccording to claim 41, wherein said step of forming the buffer layerincludes forming a buffer layer composed of Al_(x) Ga _(1−x) N, and theAl composition ratio x of said buffer layer is larger than 0 and at most1.
 57. The method according to claim 108, wherein said step of formingthe buffer layer includes forming a buffer layer having an Alcomposition ratio x of not smaller than 0.4 nor larger than 0.6.
 58. Themethod according to claim 41, wherein said step of forming the activelayer includes forming an active layer composed of InGaN.
 59. The methodaccording to claim 41, wherein said step of forming the active layerincludes forming said active layer at a growth temperature of not lowerthan 700° C. nor higher than 950° C.
 60. The method according to claim41, wherein said step of forming the second cladding layer includesforming said second cladding layer at a growth temperature of not lowerthan 1000° C. nor higher than 1200° C.
 61. The method according to claim41, wherein said step of forming the first cladding layer includesforming a first cladding layer composed of AlGaN.
 62. The methodaccording to claim 41, wherein said step of forming the cap layerincludes forming said cap layer at a growth temperature substantiallyequal to or lower than that of said active layer.
 63. The methodaccording to claim 41, wherein said step of forming the cap layerincludes forming said cap layer at a growth temperature not lower than700° C. nor higher than 950° C.
 64. The method according to claim 41,wherein said step of forming the underlayer includes forming an undopedunderlayer.
 65. The method according to claim 41, wherein said step offorming the buffer layer includes forming a non-single crystallinebuffer layer.
 66. The method according to claim 41, wherein said step offorming the underlayer includes forming a single crystalline underlayer.67. The method according to claim 41, wherein said step of forming thecap layer includes forming a cap layer composed of AlGaN.
 68. The methodaccording to claim 67, wherein said step of forming the cap layerincludes forming the cap layer containing Al.
 69. The method accordingto claim 41, wherein said step of forming the cap layer includes forminga cap layer having a band gap larger than that of said active layer. 70.A method of manufacturing a light emitting device, comprising, in thefollowing order, the steps of: forming a buffer layer composed of anitride based compound semiconductor on a substrate; forming anunderlayer composed of a nitride based compound semiconductor; forming acontact layer composed of a first conductivity type; forming a firstcladding layer composed of a nitride based compound semiconductor of thefirst conductivity type; forming an active layer having a quantum wellstructure including a quantum well layer and a quantum barrier layer andcomposed of a nitride based compound semiconductor containing indium;and forming a second cladding layer composed of a nitride based compoundsemiconductor of a second conductivity type at a growth temperaturehigher than that of said active layer.
 71. The method according to claim70, wherein said step of forming the contact layer of the firstconductivity type includes forming said contact layer of the firstconductivity type at a growth temperature of not lower than 1000° C. norhigher than 1200° C.
 72. The method according to claim 70, furthercomprising the step of forming a contact layer of the secondconductivity type on said second cladding layer.
 73. The methodaccording to claim 70, wherein said step of forming the contact layer ofthe second conductivity type includes forming a contact layer of thesecond conductivity type composed of GaN.
 74. The method according toclaim 70, wherein said step of forming the active layer includes forminga quantum well layer composed of In_(s) Ga _(1−s) N wherein 1>s>0. 75.The method according to claim 70, wherein said step of forming theactive layer includes forming a quantum well layer composed of In_(s) Ga_(1−s) N wherein 1>s>0, and a quantum barrier layer composed of In _(r)Ga _(1−r) N wherein 1>s>r≧0.
 76. The method according to claim 70,wherein said step of forming the second cladding layer includes forminga second cladding layer composed of AlGaN.
 77. The method according toclaim 70, wherein said step of forming the underlayer includes formingan underlayer composed of Al_(y) Ga _(1−y) N, and the Al compositionratio y of said underlayer is at least 0 and smaller than
 1. 78. Themethod according to claim 70, wherein said step of forming the bufferlayer includes forming a buffer layer composed of Al_(x) Ga _(1−x) N,and the Al composition ratio x of said buffer layer is larger than 0 andat most
 1. 79. The method according to claim 70, wherein said step offorming the buffer layer includes forming a buffer layer having an Alcomposition ratio x of not smaller than 0.4 nor larger than 0.6.
 80. Themethod according to claim 70, wherein said step of forming the activelayer includes forming an active layer composed of InGaN.
 81. The methodaccording to claim 70, wherein said step of forming the active layerincludes forming said active layer at a growth temperature of not lowerthan 700° C. nor higher than 950° C.
 82. The method according to claim70, wherein said step of forming the second cladding layer includesforming said second cladding layer at a growth temperature of not lowerthan 1000° C. nor higher than 1200° C.
 83. The method according to claim70, wherein said step of forming the first cladding layer includesforming a first cladding layer composed of AlGaN.
 84. The methodaccording to claim 70, wherein said step of forming the underlayerincludes forming an undoped underlayer.
 85. The method according toclaim 70, wherein said step of forming the buffer layer includes forminga non-single crystalline buffer layer.
 86. The method according to claim70, wherein said step of forming the underlayer includes forming asingle crystalline underlayer.